The employee notice of appeal must be sent to the person identified in the process you have been involved in. If in doubt, check with your HR lead.
The safest way to serve notice is to deliver in person or failing this, is to send by courier, post or email.
In person: hand the letter to your contact personally.
Post: if you are posting the letter, then it is recommended that you use recorded delivery and that you keep a copy of the proof of posting and delivery.
Email: request a "read receipt" as proof of delivery.